“The most striking finding of this study was that even though heart disease was number 1 in terms of mortality burden as a whole worldwide, there are a substantial minority of countries where stroke is a larger burden than heart disease and many of these countries are in the developing world,” said lead author Anthony S. Kim, MD, assistant professor of neurology, University of California, San Francisco.

China has an “eye-opening” stroke mortality rate, say researchers.

China in particular is a “big outlier” when it comes to stroke burden relative to heart disease, said Dr. Kim. “The high mortality from stroke in this nation far outpaces ischemic heart disease, which is the exact opposite of the situation in the US, where heart disease outstrips stroke as a cause of death.”

The new study suggests that the greater stroke burden in developing areas of the world may be due to lower national income and vascular risk factors.

Researchers used data on mortality and rates of disability-adjusted life-years lost from stroke and ischemic heart disease from 192 World Health Organization (WHO) member countries. They also accessed national estimates of risk factors developed by the WHO Burden of Disease Program and income data from World Bank estimates.

Stroke Mortality

The study showed that mortality rates due to stroke varied from country to country. The rate ranged from 25 per 100,000 in Seychelles to 249 per 100,000 in Kyrgyzstan.

Although heart disease mortality rates generally exceeded those from stroke across the globe, 74 countries, many in Africa and Asia, had stroke mortality rates that were higher. For example, Kiribati, a small island nation in the South Pacific, had a mortality rate due to stroke of 143 per 100,000 that was 11 times higher than that for heart disease (13 per 100,000).

Kiribati’s ischemic heart disease mortality rate was the lowest, but at the other end of the scale, rates were relatively high in the Middle East and Europe. The highest rate was 456 per 100,000 in Turkmenistan. Azerbaijan had a heart disease mortality rate that was more than 3 times higher than that due to stroke: 2933 per 100,000 vs 843 per 100,000.

China was at the top of the list in terms of mortality from stroke compared with heart disease, coming in second only to Kiribati. China had a stroke mortality rate of 157 per 100,000, compared with a heart disease mortality rate of 63 per 100,000. It’s not clear from this study why China would be such an outlier, but other research shows the rate could be related to a higher proportion of hemorrhagic strokes vs ischemic strokes, Dr. Kim said.

He pointed to Japan as an interesting parallel. “In the past, Japan had a very similar pattern of stroke being more of an issue than heart disease, but as that society has developed over the past few decades, the pattern is looking more and more like a typical US western pattern, so heart disease has become more of an issue.”

Dr. Kim speculated that this change might be due to improved treatment of extremely high blood pressure. “That may also be borne out in China, where very high blood pressures of folks that are undiagnosed and untreated may contribute more to stroke than to heart disease.”

Disease Burden

Disease burden from stroke also varied globally, ranging from 175 disability-adjusted life-years lost per 100,000 in Seychelles to 2078 life-years lost per 100,000 in Kyrgyzstan. Disease burden from heart disease ranged from 145 years lost per 100,000 in Kiribati to 4259 years lost per 100,000 in Afghanistan.

Worldwide, disease burden from heart disease was greater than the burden from stroke, but this was not the case in 62 countries (32%), including China, Mongolia, Haiti, and Thailand, where the burden from stroke was greater.

Vascular risk factors such as diabetes, cholesterol levels, and body mass index played a role in the differences in relative rates of stroke mortality, but living standards also contributed.

“People tend to assume that the differences in the relative amounts of stroke and heart disease are mostly driven by differences in risk factors; so less well-controlled hypertension, diabetes, and the other typical risk factors for vascular disease would explain the differences in burdens,” said Dr. Kim. “But one of the surprising findings of the study is that availability of resources as measured by national income has a much stronger influence on disease burden. This is because it probably affects other aspects that are separate from just the biology, including access to care and access to treatment.”

The burden of stroke and heart disease in developing countries highlighted by this study is something of an eye-opener because these diseases are often considered illnesses of the western world. The finding runs contrary to the “typical notion” that infectious disease is the primary burden in developing nations, said Dr. Kim.

The recognition of this burden should help prioritize public health resources and determine where to allocate such resources for prevention and treatment, said Dr. Kim. “Knowing about the distribution as well as identifying outliers, and then maybe later going back in and understanding what’s going on in those particular countries to make the relative disease burden so different than the overall pattern, could be informative,” Dr. Kim said.

United Nations Meeting

In an accompanying editorial, Sidney C. Smith Jr., MD, professor of medicine and director of the Center of Cardiovascular Science and Medicine, University of North Carolina at Chapel Hill, said the global variation in cardiovascular disease mortality and the high stroke burden in some lower-income countries should be topics for discussion at a major upcoming United Nations meeting.

The aim of the September meeting is to determine priority actions and interventions in response to rising rates of noncommunicable diseases, including cardiovascular disease around the world.

Quite striking.

The meeting “represents an unprecedented opportunity for those involved in the prevention and treatment of cardiovascular disease and all other concerned parties, including the member nations of the United Nations and their health ministries, to act and initiate priority programs and interventions that can avert the evolving pandemic of cardiovascular disease and address the devastating worldwide effects of non-communicable diseases,” wrote Dr. Smith.

Approached for a comment on the study, Seemant Chaturvedi, MD, professor of neurology at Wayne State University School of Medicine in Detroit, Michigan, and a member of the American Academy of Neurology, said the paper is a reminder of the significant geographic variation in stroke and heart disease rates.

The high stroke burden in China is “quite striking,” he said in an email to Medscape Medical News.

“Further studies are needed to address which treatable risk factors are most prevalent in each country,” said Dr. Chaturvedi. “For example, in some countries, diabetes may be the main target whereas in other locales, treating hypertension and smoking cessation may give the biggest bang for the buck.”

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